Field of the Invention and Related Background Art
The present invention relates to a dispersing agent for a pigment (hereinafter often xe2x80x9cpigment-dispersing agentxe2x80x9d) which is to improve dispersibility of pigments, and a pigment-dispersion composition incorporating the same. The present invention also relates to a toner for developing electrostatic images for image-forming methods, e.g., electrophotography and electrostatic printing, or for forming toner images in a toner-jet type image-forming method, and to a process for producing the same. In particular, the present invention relates to a toner for fixing images formed by the toner on a transfer medium under heating and pressure, and to a process for producing the same.
In processes for producing products, e.g., coating material, ink, toner and formed resin article, a pigment-dispersing agent has been effectively utilized as an additive for finely dividing a pigment and thereby sufficiently realizing its colorant performances (e.g., coloring capacity, transparency and gloss).
A pigment-dispersing agent should satisfy various requirements to fully exhibit its functions, e.g., chemical structure which fast adsorbs a pigment in the molecule, affinity for a solvent and resin which are used to disperse the pigment, and chemical structure which provides steric hindrance to prevent re-agglomeration of the pigment. A phthalocyanine-based pigment and carbon black incorporate a phthalocyanine-based colorant derivative. One type of known pigment-dispersing agents is prepared by mixing a material which can adsorb a pigment with a resin which has affinity for the solvent and resin and can provide steric hindrance, and bonding them to each other by acid-base interactions, in order to make the pigment commonly applicable to a variety of solvents and resins (disclosed in, e.g., Japanese Patent Application Laid-Open No. 06-122835, Japanese Patent Application No. 09-5989 and National Publication No. 2002-514263).
However, when such a two-component pigment-dispersing agent is used, it is necessary to prepare it under conditions which cause no scission of the bond of acidic and basic groups bonding them to each other, and to keep these conditions. When a pigment is dispersed in an aqueous solvent, in particular, sufficient care must be taken for a solvent pH level and a functional group of the resin to be incorporated. Even when they are dissociated from each other, dispersed conditions can be kept to some extent by the actions of a polar group of the phthalocyanine derivative. However, this may cause problems, e.g., re-agglomeration of the pigment or floating of the pigment in the presence of the polar group in the subsequent steps, e.g., drying, molding and polymerization.
Toners for printers and copying machines are composed of toner particles with a binder resin, colorant (e.g., magnetic particles, carbon black, dye or pigment) and wax as the main ingredients, and the toner particles generally have a weight-average particle diameter of 4 to 20 xcexcm. In general, the toner particles are prepared by melting a mixture of a thermoplastic resin and a colorant to uniformly disperse the colorant in the resin, finely dividing the mixture after it is cooled, and classifying the resultant particles to produce particles of a desired particle diameter. The colorant is uniformly dispersed in the thermoplastic resin by, e.g., kneading or flushing, where a pigment-dispersing agent is expected to increase dispersibility of the pigment, when mixed with the colorant and the thermoplastic resin. However, the pigment-dispersing agent may adversely affect electrification characteristics of the toner particles, because it must be incorporated at 20 to 50% by weight based on the pigment.
Suspension polymerization, which involves no crushing of particles, is proposed for production of toner particles (disclosed in, e.g., Japanese Patent Application Laid-Open No. 05-197193). This process comprises the steps of dissolving or dispersing a colorant, charge control agent and wax in a polymerizable monomer to prepare a polymerizable monomer composition; dispersing the composition in an aqueous solvent containing a dispersion stabilizer with a dispersion apparatus to form polymerizable monomer composition particles in the aqueous solvent; and polymerizing and solidifying the polymerizable monomer in the polymerizable monomer composition to produce toner particles of intended particle diameter and composition. This process, involving no particle crushing step, is expected to bring favorable effects, e.g., energy saving, improved process yield and reduced cost. However, the pigment particles, even when finely dispersed in the polymerizable monomer, may re-agglomerate with each other in the polymerization step, to possibly deteriorate colorant capacity and transparency of the fixed images. Use of a pigment-dispersing agent for the process is considered. However, it tends to adversely affect electrification characteristics of the toner particles, because it must be incorporated at 20 to 50% by weight based on the pigment.
One of the pigment-dispersing agents proposed to solve the above problems has a pigment-adsorbing segment covalently bonded, to a resin material segment which has affinity for the solvent and resin and provides steric hindrance (disclosed in, e.g., Japanese Patent Application Laid-Open No. 2002-226727). When a compound in which a Cu-phthalocyanine skeleton is grafted in a polymer is employed as a dispersing agent, it can exhibit the dispersion effect even in a trace quantity in the pigment, and successfully prevents re-agglomeration of the pigment particles in the polymerization step and keeps electrification characteristics of the toner. However, production of such a pigment-dispersing agent needs a multi-staged synthesis route. Therefore, there are great demands for pigment-dispersing agents which can be produced in high productivity.
Incorporation of Zn-phthalocyanine is also proposed to control a color tone of a cyan pigment (disclosed in, e.g., Japanese Patent Application Laid-Open No. 2000-302993). However, Zn-phthalocyanine, when present alone, can neither prevent re-agglomeration of pigment particles nor improve their affinity for a dispersion medium, even when it is adsorbed on the pigment particle surface. Accordingly, it will bring no effect of dispersing the pigment. Japanese Patent Application Laid-Open No. 2000-302993 also describes that a dispersing agent is incorporated preferably at 5 to 80% by weight based on a pigment. However, pigment-dispersing agents exhibiting the effect in a smaller quantity are in demand.
It is an object of the present invention to provide a dispersing agent for a pigment free of the above problems.
It is another object of the present invention to provide a dispersing agent for a pigment capable of finely dispersing, in a smaller quantity, pigment particles in a dispersion medium.
It is another object of the present invention to provide an inexpensive dispersing agent for a pigment not involving a multi-staged synthesis route.
It is still another object of the present invention to provide a pigment-dispersion composition capable of keeping pigment particles stably dispersed in various production steps after the pigment is incorporated in the raw material.
It is still another object of the present invention to provide a toner in which a pigment can be finely dispersed in the toner particles and which is excellent in coloring capacity and transparency, and a process for producing the same.
It is still another object of the present invention to provide a toner free of colorant floating on a toner particle surface and excellent in electrification characteristics and environmental stability, and a process for producing the same.
The present invention relates to a dispersing agent for a pigment comprising at least
a metallic compound having a structure represented by the general formula (I): 
(wherein, X1 to X4 are each independently a nitrogen atom or Cxe2x80x94R (R is a hydrogen atom, or an alkyl group of 1 to 12 carbon atoms, which may have a substituent, or an aromatic hydrocarbon group, which may be substituted); Y1 to Y8 are each independently a hydrogen atom or an alkyl group of 1 to 12 carbon atoms, which may be substituted; or Y1 and Y2, Y3 and Y4, Y5 and Y6 and/or Y7 and Y8 constitute an aromatic hydrocarbon ring which may have a substituent; and M is a metal capable of taking a penta-coordinated structure) and
an n-electron-donating compound capable of being coordinated with the central metal of the metallic compound.
The present invention also relates to a pigment-dispersion composition comprising at least
a dispersing agent for a pigment which comprises at least a metallic compound having a structure represented by the general formula (I): 
(wherein, X1 to X4 are each independently a nitrogen atom or Cxe2x80x94R (R is hydrogen atom, or an alkyl group of 1 to 12 carbon atoms, which may have a substituent, or an aromatic hydrocarbon group, which may be substituted); Y1 to Y8 are each independently a hydrogen atom or an alkyl group of 1 to 12 carbon atoms, which may be substituted; or Y1 and Y2, Y3 and Y4, Y5 and Y6 and/or Y7 and Y8 constitute an aromatic hydrocarbon ring which may have a substituent; and M is a metal capable of taking a penta-coordinated structure) and an n-electron-donating compound capable of being coordinated with the central metal of the metallic compound,
a pigment, and
a dispersion medium.
The present invention also relates to a toner containing toner particles comprising at least
a dispersing agent for a pigment which comprises at least a metallic compound having a structure represented by the general formula (I): 
(wherein, X1 to X4 are each independently a nitrogen atom or Cxe2x80x94R (R is hydrogen atom, or an alkyl group of 1 to 12 carbon atoms, which may have a substituent, or an aromatic hydrocarbon group, which may be substituted); Y1 to Y8 are each independently a hydrogen atom or an alkyl group of 1 to 12 carbon atoms, which may be substituted; or Y1 and Y2, Y3 and Y4, Y5 and Y6 and/or Y7 and Y8 constitute an aromatic hydrocarbon ring which may have a substituent; and M is a metal capable of taking a penta-coordinated structure) and an n-electron-donating compound capable of being coordinated with the central metal of the metallic compound,
a pigment, and
a binder resin.
The present invention also relates to a process for producing a toner comprising a step of mixing
a dispersing agent for a pigment which comprises at least a metallic compound having a structure represented by the general formula (I): 
(wherein, X1 to X4 are each independently a nitrogen atom or Cxe2x80x94R (R is hydrogen atom, or an alkyl group of 1 to 12 carbon atoms, which may have a substituent, or an aromatic hydrocarbon group, which may be substituted); Y1 to Y8 are each independently a hydrogen atom or an alkyl group of 1 to 12 carbon atoms, which may be substituted; or Y1 and Y2, Y3 and Y4, Y5 and Y6 and/or Y7 and Y8 constitute an aromatic hydrocarbon ring which may have a substituent; and M is a metal capable of taking a penta-coordinated structure) and an n-electron-donating compound capable of being coordinated with the central metal of the metallic compound, and
a pigment.
The inventors of the present invention have found, after having extensively studied, that a dispersing agent for a pigment comprising a metallic compound of specific structure and a compound capable of being coordination-bonded at the central metal of the metallic compound can easily disperse a pigment finely in a dispersion medium, achieving the present invention.
The pigment-dispersing agent of the present invention can be used in processes for producing products, e.g., coating material, ink, toner and formed resin article, as a pigment-treating agent to improve dispersibility of the pigment. The pigment-dispersing agent of the present invention is characterized by comprising a metallic compound of specific structure which allows the central metal to take a penta-coordinated structure and an n-electron-donating compound capable of being coordinated with the central metal of the metallic compound.
The pigment-dispersing agent of the present invention comprises a metallic compound whose central metal, which is to be adsorbed on the pigment, is coordination-bonded to an n-electron-donating compound having a prevention of re-agglomeration of pigments and a dispersing effect, produced by mixing and dispersing these components. The n-electron-donating compound, which can work as a ligand, has affinity for the dispersion medium to produce an excellent dispersion effect.
The metallic compound has a structure represented by the general formula (I): 
(wherein, X1 to X4 are each independently a nitrogen atom or Cxe2x80x94R (R is hydrogen atom, or an alkyl group of 1 to 12 carbon atoms, which may have a substituent, or an aromatic hydrocarbon group, which may be substituted); Y1 to Y8 are each independently a hydrogen atom or an alkyl group of 1 to 12 carbon atoms, which may be substituted; or Y1 and Y2, Y3 and Y4, Y5 and Y6 and/or Y7 and Y8 constitute an aromatic hydrocarbon ring which may have a substituent; and M is a metal capable of taking a penta-coordinated structure).
The substituent is not limited. The examples include those having a carboxylic, sulfonic, aromatic-based, aliphatic-based, ether or alcohol group introduced. However, those hindering adsorptivity with the pigment or easy inclusion of a ligand for coordination in the axial direction are not desirable. Undesirable substituents include functional groups whose amine by itself can become a ligand, and those having a side chain which may cause steric hindrance on the plane on which the pigment is to be adsorbed.
In consideration of adsorptivity with the pigment, the metallic compound preferably has a phthalocyanine skeleton represented by the general formula (I) with X1 to X4 being each independently a nitrogen atom, and each of combinations of Y1 and Y2, Y3 and Y4, Y5 and Y6, and Y7 and Y8 constitutes an aromatic hydrocarbon ring which may have a substituent.
The metal as the central metal M in the metallic compound is aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, germanium, palladium, cadmium, indium, tin, platinum or lead, in consideration of the ligand to be coordinated in the axial direction. The penta-coordinated structure is particularly preferable in a presence of a ligand, because it can be coordination-bonded to the plane on which the pigment is adsorbed. Of the above metals, zinc takes the penta-coordinated structure more easily than the others.
Moreover, of the metallic compounds with zinc as the central metal, zinc-phthalocyanine (Zn-phthalocyanine) represented by the following formula is most preferable, in consideration of its fastness as a pigment-dispersing agent and adsorptivity with a phthalocyanine pigment: 
In the present invention, zinc-phthalocyanine is contained as the pigment-adsorbing segment in the pigment-dispersing agent, and can achieve its role at a very low content, sufficiently exhibiting its effect at 5% by weight or less. The effect of adjusting color tone which zinc-phthalocyanine itself has is in a negligible range.
The n-electron-donating compound capable of being coordinated with the central metal of the metallic compound is not limited. The compound having an excellent n-electron-donating property preferably has at least one skeleton selected from the group consisting of primary to tertiary amines, imines, primary to tertiary amides, imides, aromatic imides (e.g., pyridine), thiols, thioesters, thionyl, sulfide and sulfoxide. The unshared electron pair in the nitrogen or sulfur atom in these skeletons shows excellent coordination capacity, and can be easily designed as the ligand.
The n-electron-donating compound is preferably an oligomer or polymer, because of its affinity for the dispersion medium and steric hindrance it provides against the pigment to make it dispersible. The oligomers or polymers useful for the present invention include styrene copolymers of a styrene monomer and an n-electron donative monomer, copolymers of an acrylic monomer and an n-electron donative monomer and copolymers of a methacrylic monomer and an n-electron donative monomer; copolymers of an ester-based monomer and an n-electron donative monomer; copolymers of an ether-based monomer and an n-electron donative monomer; copolymers of a vinyl alcohol monomer and an n-electron donative monomer; and copolymers of a vinyl butyral monomer and an n-electron donative monomer. Moreover, polyurethanes and polypeptides are also useful for the present invention.
The pigment for the present invention may be selected from known ones. In particular, the pigment-dispersing agent of the present invention can be effectively utilized for colored pigments, e.g., phthalocyanine-based pigment, and carbon black.
As phthalocyanine-based pigments, copper-phthalocyanine (Cu-phthalocyanine) represented by the following formula is preferable. 
The dispersion medium for the present invention is selected depending on specific purposes of the pigment-dispersion composition, and is not limited. More specifically, the media useful for the present invention include water; alcohols, e.g., methyl alcohol, ethyl alcohol, modified ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, tert-amyl alcohol, 3-pentanol, octyl alcohol, benzyl alcohol and cyclohexanol; ether alcohols, e.g., methyl cellosolve, cellosolve, isopropyl cellosolve, butyl cellosolve, diethylene glycol and monobutyl ether; ketones, e.g., acetone, methylethylketone and methylisobutylketone; esters, e.g., ethyl acetate, butyl acetate, ethyl propionate and cellosolve acetate; hydrocarbons, e.g., hexane, octane, petroleum-derived ether, cyclohexane, benzene, toluene and xylene; halogenated hydrocarbons, e.g., carbon tetrachloride, trichloroethylene and tetrabromoethane; ethers, e.g., ethyl ether, dimethyl glycol and trioxanetetrahydrofuran; acetals, e.g., methylal and diethyl acetal; organic acids, e.g., formic acid, acetic acid and propionic acid; and organic compounds containing sulfur or nitrogen, e.g., nitropropene, nitrobenzene, dimethylamine, monoethanolamine, pyridine, dimethyl sulfoxide and dimethyl formamide. Moreover, the dispersion medium may be a resin. More specifically, the resins useful for the present invention include polystyrene and styrene copolymer; polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, acrylate copolymer and methacrylate copolymer; polyester; polyvinyl ether and polyvinyl methyl ether; and polyvinyl alcohol and polyvinyl butyral. Still more, polyurethane and polypeptide are also useful for the present invention. These dispersion media may be used either individually or in combination.
The polymerizable monomer useful as the dispersion medium for the present invention is for addition or condensation polymerization, that for the former being more preferable. More specifically, the polymerizable monomers useful for the present invention include styrene; styrene derivatives, e.g., o-methyl styrene, m-methyl styrene, p-methyl styrene, p-methoxystyrene, p-phenyl styrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethyl styrene, 2,4-dimethyl styrene, p-n-butyl styrene, p-tert-butyl styrene, p-n-hexyl styrene, p-n-octyl styrene, p-n-nonyl styrene, p-n-decyl styrene and p-n-dodecyl styrene; ethylenic unsaturated monoolefins, e.g., ethylene, propylene, butylenes and isobutylene; unsaturated polyenes, e.g., butadiene and isoprene; halogenated vinyls, e.g., vinyl chloride, vinylidene chloride, vinyl bromide and vinyl iodide; vinyl esters, e.g., vinyl acetate, vinyl propionate and vinyl benzoate; xcex1-methylene fatty acid/monocarboxylic acid esters, e.g., methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; acrylate esters, e.g., methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate and phenyl acrylate; vinyl ethers, e.g., vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; N-vinyl compounds, e.g., vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone; vinyl naphthalene; and acrylic acid derivatives, e.g., acrylonitrile, methacrylonitrile and acrylamide.
As described above, the pigment-dispersing agent of the present invention comprises a metallic compound of specific structure, whose central metal can take a penta-coordinated structure, and n-electron-donating compound capable of being coordinated with the central metal of the metallic compound. It can be produced by separately charging the metallic compound and n-electron-donating compound working as the ligand in the dispersion medium, before the pigment is dispersed in the medium by utilizing the coordination bond. This means that the metallic compound segment as the pigment-adsorbing segment and ligand segment for providing dispersibility can be individually prepared, thereby facilitating synthesis of the pigment-dispersing agent of the present invention.
The pigment-dispersion composition of the present invention comprises at least a dispersion medium, pigment and the pigment-dispersing agent of the present invention. In other words, a known pigment and dispersion medium can be suitably used for the pigment-dispersion composition of the present invention.
For the production of the pigment-dispersion composition of the present invention, the pigment-dispersing agent and, as required, a resin are dissolved in a dispersion medium, to which a powdered pigment is added little by little with stirring to be sufficiently compatible with the medium. The pigment-dispersing agent can be adsorbed on the pigment particle surfaces under a mechanical shear force by a disperser, e.g., ball mill, paint shaker, dissolver, attritor, sand mill or high-speed mill, to finely re-disperse the pigment in the form of stably uniform, fine particles in the medium.
The toner of the present invention is for developing electrostatic images, or for forming toner images in a toner-jet type image-forming method. In particular, it is suitable for an image-forming method involving fixation of the toner images on a transfer medium under heating and pressure.
The toner of the present invention is characterized by comprising at least the pigment-dispersing agent of the present invention. The process of the present invention for forming the toner uses the pigment-dispersing agent of the present invention in the pigment dispersing step.
When the toner is produced by a crushing process, the pigment-dispersing agent of the present invention, a pigment, binder resin as the dispersion medium and one or more additives are sufficiently mixed with each other by a mixer, e.g., Henschel mixer or ball mill. The mixture is then melt-kneaded by a kneader operating at elevated temperature, e.g., kneader or extruder, where it is subjected to heat and mechanical shear force to melt the resin. In this stage, the pigment particles are surface-treated with the pigment-dispersing agent and, at the same time, finely dispersed in the molten material. The molten/kneaded mixture is cooled for solidification, and preliminary crushed and then finely pulverized. The resultant fine particles pulverized are classified to obtain the toner particles.
The particles of the toner of the present invention can be produced by a polymerization process involving the polymerization step in which the polymerizable monomer composition, comprising at least a polymerizable monomer for forming the binder resin, pigment and the pigment-dispersing agent of the present invention, is polymerized with the aid of radical polymerization initiator, light or heat, and are especially preferable because they allow the pigment-dispersing agent of the present invention to exhibit its effect more efficiently.
In the process involving suspension polymerization for producing the toner particles, in particular, the pigment-dispersion composition incorporating a polymerizable monomer as the dispersion medium is treated by a disperser, to prepare the pigment-dispersed paste comprising the polymerizable monomer, pigment and pigment-dispersing agent. The resultant paste is further treated by an agitator together with the polymerizable monomer, a polymerization initiator, wax and, as required, one or more other additives to prepare the polymerizable monomer composition in the form of uniform mixture or dispersion. The polymerizable monomer composition thus obtained is incorporated in the dispersion medium (preferably aqueous medium) containing a dispersion stabilizer, and finely dispersed to the toner particle size by an agitator, e.g., high-speed agitator or high-speed disperser, e.g., ultrasonic disperser (granulation step). The toner particles can be produced by polymerizing the polymerizable monomer finely dispersed in the polymerizable monomer composition in polymerization step with the aid of a radical polymerization initiator, light and/or heat.
For production of the toner of the present invention, an additive may be externally added in the toner particles during the production process.
The polymerizable monomer contained in the toner particles to form the binder resin may be the one similar to the polymerizable monomer described above.
The pigment for the toner of the present invention may be selected from known pigments. In particular, a colored pigment, e.g., phthalocyanine-based one or carbon black, is suitable for the present invention. It is incorporated preferably at 3 to 20 parts by weight based on 100 parts by weight of the polymerizable monomer.
The pigment contained in the toner of the present invention is surface-treated with the pigment-dispersing agent of the present invention, described above. The pigment-dispersion paste containing the pigment surface-treated with the pigment-dispersing agent of the present invention can be produced by treating the pigment-dispersion composition of the present invention by a varying pigment disperser. The optimum content of the pigment-dispersing agent depends on the desired particle size of the dispersed pigment. It is incorporated preferably at 0.3 parts by weight or more based on 100 parts by weight of the pigment, in order to sufficiently adsorb the metallic compound serving as the pigment-adsorbing segment on the pigment particle surfaces. At an excessively high content, the metallic compound itself develops a color to affect color phase of the pigment. In consideration of the above, the metallic compound as one of the components of the pigment-dispersing agent contained in the toner is incorporated preferably at 0.01 to 2.5% by weight, more preferably 0.01 to 1.0% by weight, based on the weight of the toner.
The n-electron-donating compound, which is coordinated with the central metal of the metallic compound to provide steric hindrance and thereby to prevent re-agglomeration of the pigment particles with each other, is preferably a polymer in the toner. The polymer preferably has a weight-average molecular weight Mw of 2,000 to 100,000 to produce the dispersion effect while causing no damage on the toner""s fixing performance. Increasing content of the n-electron-donating compound is preferable, viewed from efficiency of its coordination with the metallic compound. However, an excessively high content is undesirable in consideration of its effects on the toner properties. Based on these considerations, the n-electron-donating compound is incorporated preferably at 0.05 to 10% by weight based on the weight of the toner.
Moreover, when the pigment dispersion medium is a binder resin for the toner or polymerizable monomer for forming the binder resin of the toner, the n-electron-donating compound preferably has at least one type of the polymerizable monomer unit which constitutes the binder resin and n-electron donative, polymerizable monomer unit, because it produces an excellent pigment dispersion effect by its affinity for the dispersion medium, and keeps the pigment well dispersed in the polymerization step. For example, when the binder resin is a styrene/butyl acrylate copolymer, a styrene/vinyl pyridine copolymer is cited as a preferable polymer serving as the n-electron-donating compound. Moreover, it can bring the n-electron-donating compound""s properties close to those of the binder resin, thereby controlling the adverse effects on the toner""s properties. Increasing number of the functional groups capable of being coordinated is preferable, viewed from the considerations including coordination efficiency. Based on these considerations, the n-electron-donating compound is preferably a polymer which contains the n-electron donative, polymerizable monomer unit at 0.1 to 30% by weight, more preferably 1.0 to 10% by weight, when it is to be used for toner.
The toner containing the pigment surface-treated with the pigment-dispersing agent of the present invention can be produced by suspension polymerization, where the pigment-dispersion paste containing the pigment-dispersing agent of the present invention is mixed with a polymerizable monomer, polymerization initiator and one or more other additives, and the resultant polymerizable monomer composition is dispersed in an aqueous dispersion medium.
The aqueous dispersion medium useful for the process involving suspension polymerization for production of the toner of the present invention is selected mainly according to the polymerizable monomer used and solubility of the resultant polymer. More specifically, those media useful for the present invention include water; alcohols, e.g., methyl alcohol, ethyl alcohol, modified ethyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, sec-butyl alcohol, tert-amyl alcohol, 3-pentanol, octyl alcohol, benzyl alcohol and cyclohexanol; ether alcohols, e.g., methyl cellosolve, cellosolve, isopropyl cellosolve, butyl cellosolve, diethylene glycol and monobutyl ether; ketones, e.g., acetone, methylethylketone and methylisobutylketone; esters, e.g., ethyl acetate, butyl acetate, ethyl propionate and cellosolve acetate; hydrocarbons, e.g., hexane, octane, petroleum-derived ether, cyclohexane, benzene, toluene and xylene; halogenated hydrocarbons, e.g., carbon tetrachloride, trichloroethylene and tetrabromoethane; ethers, e.g., ethyl ether, dimethyl glycol and trioxanetetrahydrofuran; acetals, e.g., methylal and diethyl acetal; organic acids, e.g., formic acid, acetic acid and propionic acid; and organic compounds containing sulfur or nitrogen, e.g., nitropropene, nitrobenzene, dimethylamine, monoethanolamine, pyridine, dimethyl sulfoxide and dimethyl formamide. These media may be used either individually or in combination. The polymerizable monomer is incorporated at 1 to 80% by weight, preferably 10 to 65% by weight, based on the weight of the medium.
The dispersion stabilizer for the toner particles, useful for the process involving suspension polymerization for production of the toner of the present invention, may be selected from the known ones. More specifically, these stabilizers include inorganic compounds, e.g., calcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate, bentonite, silica and alumina; and organic compounds, e.g., polyvinyl alcohol, gelatin, methyl cellulose, methylhydroxypropyl cellulose, ethyl cellulose, sodium salt of carboxymethyl cellulose; polyacrylic acid and its salt; and starch. The dispersion stabilizer is incorporated preferably at 0.2 to 20% by weight based on 100% by weight of the polymerizable monomer.
The polymerization initiator used in the process for producing the toner of the present invention may include known polymerization initiators. Stated specifically, it may include azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobis-(2,4-dimethylvaleronitrile), 2,2xe2x80x2-azobis(2-methylbutyronitrile), 1,1xe2x80x2-azobis-(cyclohexane-1-carbonitrile), dimethyl-2,2xe2x80x2-azobisisobutyrate, 4,4xe2x80x2-azobis-4-cyanovaleronitrile and 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile); peroxides such as benzoyl peroxide, and methyl ethyl ketone peroxide; nucleophilic reagents such as alkali metals, metal hydroxides and Grignard reagents; and protonic acid, metal halides and stabilized carbonium ions. The polymerization initiator may preferably be in a concentration of from 0.1 to 20% by weight, and more preferably from 0.1 to 10% by weight, based on the weight of the monomer.
In the case when the toner of the present invention is produced by polymerization, a chain transfer agent may be used, which may include known chain transfer agents.
In the present invention, toner additives as shown below may further be used in order to provide the toner with various properties.
In order to stabilize triboelectric charging performance of the toner, a charge control agent may be incorporated in the toner particles. In this case, it is preferable to use a charge control agent having a high toner charging speed and capable of maintaining a constant charge quantity stably. When the polymerization method is used to produce the toner particles, charge control agents having no polymerization inhibitory action are particularly preferred. Stated specifically, as negative charge control agents, preferred are metal compounds of salicylic acid, alkyl salicylic acids, dialkyl salicylic acids, naphthoic acid or dicarboxylic acids, polymer type compounds having sulfonic acid or carboxylic acid in the side chain, boron compounds, urea compounds, silicon compounds and carixarene. As positive charge control agents, preferred are quaternary ammonium salts, polymer type compounds having such a quaternary ammonium salt in the side chain, guanidine compounds, and imidazole compounds. Any of these charge control agents may preferably be added in a amount of from 0.5 to 10 parts by weight based on 100 parts by weight of the binder resin.
Additives such as a fluidity-providing agent, an abrasive, a lubricant and charge controlling particles may also externally be added to the toner particles.
As the fluidity-providing agent, metal oxides such as silicon oxide, aluminum oxide and titanium oxide may preferably be used. These may more preferably be those having been subjected to hydrophobic treatment. As the abrasive, metal oxides such as cerium oxide, aluminum oxide, magnesium oxide and chromium oxide, nitrides such as silicon nitride, carbides such as silicon carbide, and metal salts such as strontium titanate, calcium sulfate, barium sulfate and calcium carbonate may preferably be used. As the lubricant, fluorine resin powders such as vinylidene fluoride and polytetrafluoroethylene, and fatty acid metal salts such as zinc stearate and calcium stearate may preferably be used. As the charge controlling particles, metal oxides such as tin oxide, titanium oxide, zinc oxide, silicon oxide and aluminum oxide, and carbon black may preferably be used.
Any of these external additives may be used in an amount of from 0.1 part to 10 parts by weight, and preferably from 0.1 part to 5 parts by weight, based on 100 parts by weight of the toner particles. These additives may be used alone or in combination of two or more types.
The toner of the present invention may be used as an one-component developer, or may be blended with a carrier so as to be used as a two-component developer.
The measuring method of triboelectric charge quantity of the toner by means of blow-off method used in the present invention is described below.
The toner and the carrier are placed in 100 ml container made of polyethylene and are blended in a suitable blend quantity (2 to 15% by weight) when made into a developer, and are blended with a Turbula mixer for 180 seconds. This blended powder (developer) is put in a container made of a metal at the bottom of which a conductive screen of 635 meshes is provided, and then sucked by means of a suction device. The triboelectric charge quantity of the toner is determined from the difference in weight before and after the suction and from the potential accumulated in a capacitor connected to the container. Here, suction pressure is set at 250 mmHg. By this method, the triboelectric charge quantity (Q) is calculated according to the following expression.
Q(xcexcC/g)=(Cxc3x97V)/(W1xe2x88x92W2)
wherein W1 is the weight before suction, W2 is the weight after suction, C is the capacity of the capacitor, and V is the potential accumulated in the capacitor.